1. Field of the Invention
This invention relates generally to the field of ice making apparatus and more particularly to a new and improved apparatus for making ice slabs and thereafter dividing the same into cubes.
2. Brief Description of the Prior Art
Prior to the present invention it has been known to form slabs of ice on an inclined refrigerated plate assembly associated with a mechanically driven refrigerant compressor to cool the plate below freezing while water is circulated thereover. Once a slab of ice of preselected thickness is formed the plate is heated to release the slab onto a heated grid for separation into individual cubes which are collected in a storage bin. The most current prior art in this field is represented by U.S. Pat. No. 4,154,063 which issued on May 15, 1979, to the applicant herein.
Prior art commercial ice making machines employ a large volume of refrigerant (usually refrigerant no. 12) charge. This is done in order to provide a liquid/vapor state in the evaporator tubes. As heat is transferred from the water or ice through the plate to the evaporator tubes the refrigerant is boiled off into the vapor state. Since there is an excess of liquid refrigerant, not all of it is vaporized in the formation of the ice slab. Residual liquid refrigerant is thus free to re-enter the compressor. The refrigerant, being an excellent solvent, causes the compressor lubricating oil to foam and eventually washes the oil from the compressor bearings. Even compressors designed to operate with liquid refrigerants suffer from reduced operating life for this reason.
In using the fully charged or flooded evaporator type refrigeration systems, the volume of refrigerant to be compressed is unnecessarily high and requires an oversize (high energy consuming) compressor and a condenser having a capacity which must exceed the BTU output of the compressor. A further drawback is that the volume of water through the condenser to cool the refrigerant after compression is excessive.
Ice makers of the prior art typically have evaporator assemblies incorporating inclined plates formed of high thermal conductivity materials such as copper, brass or aluminum. With such an arrangement, as water is circulated over the plate, ice is formed in thin layers over the entire surface of the plate. Since ice acts as an insulator, the heat transfer from the water to the refrigerant is progressively reduced as the ice slab thickness increases. This increases the freezing cycle time and is one of the factors giving rise to the need for a high volume of liquid refrigerant discussed above. Prior ice making machines do not use insulated evaporator tubes due to the high thermal conductivity of the plate. Such evaporator assemblies are known as the "wet" type in that atmospheric water will condense and frost or ice will form on the evaporator tubes.
Prior art ice making apparatus effect the release of an ice slab from the evaporator plate by directing hot compressor gases through the evaporator tubes. This creates undue thermal stress in the evaporator structure, tends to crack the ice slab and introduces excessive heat into the evaporator which must be removed in the next freeze cycle.
It is further known in the prior art to divide the ice slab into cubes by discharging the slab from the evaporator plate onto a heated grid. Electric wire grids have been used, however, a grid of tubing through which warm liquid refrigerant from the primary condenser is directed is considered more efficient. The tubing used in the grid is of necessity small and thin for efficient cutting and is generally soldered in holes drilled in a manifold. This type of construction is rigid but subject to failure in that the grid is repeatedly impacted by the ice slabs and must support the weight of the ice slab during the cube cutting process.
The ice makers of the prior art typically use a water manifold at the upper edge of the inclined evaporator plate and having a plurality of water discharge nozzles. The water discharge nozzles are required in order to discharge water evenly across the surface of the evaporator plate. The nozzles are subject to becoming clogged with impurities in the water and must be periodically disassembled for cleaning.